1. Field of Invention
The present invention relates to a semiconductor structure and a semiconductor device having the semiconductor structure, especially a semiconductor structure including a plurality of mitigation regions to broaden its operation voltage range and a semiconductor device having the semiconductor structure.
2. Description of Related Art
FIG. 1A shows a prior art semiconductor structure 10, wherein at least one first conductivity type well 11 and at least one second conductivity type well 12 are provided on a substrate Sub and adjacent to each other in a lateral direction indicated by a dash arrow line shown in FIG. 1A. A semiconductor device is formed in each of the first conductivity type well 11 and the second conductivity type well 12, such as a MOS transistor, BJT transistor, JFET transistor, etc., which are not shown in the figure. At least one interface region 13 is formed at the boundary between the first conductivity type well 11 and the second conductivity type well 12; the interface region 13 is a region where the first conductivity type well 11 overlaps the second conductivity type well 12. The first conductivity type well 11 and the second conductivity type well 12 are formed in an epitaxial layer on the substrate Sub. The first conductivity type well 11 is for example an N-type well and the second conductivity type well 12 is for example a P-type well; however, the first conductivity type well 11 can be a P-type well and the second conductivity type well 12 can be an N-type well. Note that the numbers of the first conductivity type well 11 and the second conductivity type well 12 and their relative positions shown in FIG. 1A are for illustrative purpose only.
When the semiconductor structure 10 is used in a high voltage device, one of the conductivity type wells such as the second conductivity type well 12 can be used to form the high voltage device, and the operation voltage range of the high voltage device is related to the breakdown voltage between the first conductivity type well 11 and the second conductivity type well 12 and the breakdown voltage between the second conductivity type well 12 and the substrate Sub. If the operation voltage is too high and the breakdown voltage is low, an electrical punch-through could penetrate the boundary between the first conductivity type well 11 and the second conductivity type well 12. FIG. 1B shows a prior art semiconductor structure 20, which includes a substrate Sub, a first conductivity type well 11, a second conductivity type well 12, an interface region 13 therebetween, and a barrier layer 24 disposed between the second conductivity type well 12 and the substrate Sub. The barrier layer 24 is provided to increase the breakdown voltage between the second conductivity type well 12 and the substrate Sub, whereby the breakdown voltage between the first conductivity type well 11 and the second conductivity type well 12 is also improved. However, the electrical punch-through may still occur to cause failure if the breakdown voltage between the first conductivity type well 11 and the second conductivity type well 12 is not high enough. The interface regions 13 shown in FIGS. 1A and 1B can improve a little of the breakdown voltage, which is not enough. Hence, it is desired to improve the breakdown voltage by a simple and effective way.